The present invention relates to a reduction gear in which a hollow space is formed in a portion of its rotation center, and more particularly to a reduction gear provided with a motor mounting portion.
As a related reduction gear, one disclosed in, for example, JP-B-8-3733U is known. This reduction gear is an eccentric oscillatory reduction gear in which an input gear for the reduction gear coupled with a hollow output shaft of a motor and a transmission gear provided on an eccentric member shaft for causing an external gear to undergo eccentric motion are combined and which has a front-stage meshing portion. The rotating shaft of this reduction gear is coaxial with the rotating shaft of the motor, and a hollow space is formed in the portion of the rotation center of the reduction gear.
With the above-described related reduction gear, however, since the wiring, piping and the like are passed in the rotating shaft of the motor which rotates at high speed, in cases where the rotating shaft of the motor is brought into contact with such wiring, piping or the like, there has been a problem in that the wiring, piping or the like is damaged.
Furthermore, in the field of reduction gears, although it is necessary to provide a rich assortment of reduction ratios to meet customer needs, even if an attempt is made to vary the reduction ratio at the front-stage meshing portion in this reduction gear, the only way to make this possible is to make the diameter of the input gear large and make the diameter of the transmission gear small. In this case, the front-stage meshing portion is undesirably set for speed increasing, so that it is impossible to provide a rich assortment of reduction ratios. Furthermore, the diameter of the input gear can be made small to set this front-stage meshing portion in a reducing relationship, but if such an arrangement is adopted, it becomes impossible to secure a hollow diameter portion.
In view of the above-described problems of the related art, the object of the invention is to provide a reduction gear which facilitates the assortment of reduction ratios of the reduction gear and is capable of having a large space in the hollow diameter portion.
The above object can be attained by a reduction gear in which a hollow space is formed in a portion of a rotation center, and the center of rotation and a rotating shaft of a motor are arranged in parallel, characterized in that a motor mounting member for maintaining a distance between the center of rotation and the rotating shaft of the motor to a fixed distance, and that a front-stage reducing portion for reducing the output rotation of the motor is provided between the center of rotation and the rotating shaft of the motor.
According to this reduction gear, the mounting of the motor is facilitated while securing a hollow space in the portion of the rotation center of the reduction gear, and the reduction ratio can be changed easily.
In addition, since an input gear member of the front-stage reducing portion is held in the motor mounting member as described in claim 2, the coupling of the motor can be effected easily by fixing the motor to the motor mounting member.
The present disclosure relates to the subject matter contained in Japanese patent application No. 2001-120321 (filed on Apr. 18, 2001), which is expressly incorporated herein by reference in its entirety.